It is herein proposed to design and develop a system that will permit the transbronchoscopic measurement of bronchial lumen diameter and subsequent bronchoscopic implantation and retrieval of a selected radiosotope capsule for localized radiotherapy of malignant lesions. Such a system of devices would not only permit an accurate determination of lumen diameter and lesion size through the flexible bronchoscope, but would also result in the development of a series of devices that could be used for a variety of applications--including low-level, long-term, localized radiotherapy to deep malignancies without the requirement for surgery. Although not designed for most cases, it is believed that such an endoscopically-introduced system would have application for the treatment of small lesions, inoperable recurring tumors, and palliation for airway maintnenace. This effort was begun several years ago and privately funded. Some early prototypes were fabricated, but funding was terminated before development and assessment was completed. During the Phase I period, it is proposed that prototypes of a measurement device together with both point source and distributed-line source radioisotopic capsule systems be fabricated and analyzed for feasibility. Testing during this period would be limited to bronchoscopic implantation and retrieval within the adult lung model recently developed and introduced for sale by Triangle Research and Development Corporation and an animal such as a goat at Johns Hopkins University School of Medicine.